A Novel Water-Soluble Phosphonate Analog of Phosphatidylinositol,D-Myo-Inositol4-(Hexadecyloxy)-3(5)-Methoxybutanephosphonate (C4-PI), Inhibits Epithelial Cell Proliferation and is a Substrate but not an Inhibitor of Phosphatidylinositol 3-Kinase

Abstract

D-myo-Inositol 4-(hexadecyloxy)-3(S)-methoxybutanephosphonate (C₄-PI), a water soluble isosteric phosphonate analog of phosphatidylinositol (PI) that is not a substrate of phosphatidylinositol-specific phospholipase C isozymes, was synthesized and was found to be phosphorylated by phosphatidyl-inositol 3-kinase (PI 3-kinase) activity immunoprecipitated from insulin-stimulated cells. The extent of phosphorylation of C₄-PI was similar to or greater than that of phosphatidylinositol, especially at higher concentrations. Since C₄-PI is very water soluble, it is an attractive tool for assaying PI kinases in vitro as no detergent or sonication is required in contrast to assays with the long-chain PI which forms micelles. The extent of phosphorylation of C₄-PI was similar or greater than that of PI, especially at higher concentrations. C₄-PI was, at best, a poor inhibitor of of PI 3-kinase activity (IC₅₀ > 150 µM). C₄-PI exhibited antiproliferative properties against the neuroblastoma cell lines SK-N-SH and SK-N-MC and the kidney carcinoma A498 cell line (IC₅₀ 20–40 µM) but had minimal effect on the proliferation of the drug-resistant ovarian adenocarcinoma Ovcar-3 line. These results indicate that the antiproliferative effect of C4-PI is unlikely to arise via inhibition of the PI 3-kinase signaling pathways in cells, however, the possibility that phosphorylated C₄-PI products interfere in PI 3-kinase cell signaling pathways cannot be ruled out.